Engine Stalling under load

I have a 1978 70Hp Evinrude that is stalling when the boat is under load. It runs fine in gear with the muffs on and no too bad on the river when its calm but in the ocean when a bit windy or with a skiier behind the boat the engine will stall when trying to accelerate.

I have replaced the fuel pump and inspected and cleaned the carbs (I thought the high speed orifice might have been clogged on one of the carbs). Compression is even 120psi across all three cylinders. All I can think of is something is stopping the prop turning as fast as it should for the corresponding throttle position(transmission) and thus the timing is out. It seems that once the boat is at speed (and prop rotating well) the motor responds perfectly.

I put the motor in gear and turned the prop. It was difficult to turn initially and a rubber friction noise was coming from the transmission. Could there be something causing friction in the transmission and thus making it hard to overcome the initial friction? Any suggestions are appreciated!!!

Re: Engine Stalling under load

The rubber friction noise could be one of two things.

1. The water pump impeller turning in the housing.

2. The rubber hub in the prop slipping.

#1 is normal, #2 is not.

Re: Engine Stalling under load

That makes sense. I tried turning a friends prop (Merc 90 hP) and there was just a ratchet noise when in gear. I assume on the Merc there is a ratchet style set up so you are not turning the flywheel when rotating the prop. Seems like on the evinrude there is no such ratchet system.

Any ideas on the stalling? I should clarify when I cleaned the carbs I only cleaned the bowls and soaked the high speed jets. I did not put a carb kit through them.

Re: Engine Stalling under load

take a permanent marker, remove the prop, draw a straight line, like the picture. take the boat for a spin, make it do what it is doing. come home remove the prop, if the lines are still line up, it is not the prop, if misaligned, the hub in the prop has slipped, and need to have a new hub installed by a prop shop, or a new prop.

do the carbs properly. http://forums.iboats.com/showthread.php?t=244013

Re: Engine Stalling under load

Stalling under load is a classic lean symtom.Sometimes a little choke will make it respond if so ; you should go through the carbs
with special attention to all jets and passages.Also check the plugs for uniform color to all.About 50% of the time when lean symtoms remain after cleaning a second more careful cleaning have success.